thermal/drivers/max77620: Remove duplicate error message

The thermal_of_zone_register() function already prints an error message
when appropriate, so remove the extra one from the MAX77620 thermal
driver.

This fixes a spurious error message when no thermal zone was defined
for the MAX77620 in device tree.

Reported-by: Nicolas Chauvet <kwizart@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20231013155104.1781197-1-thierry.reding@gmail.com